The invention relates to a method for producing energy storage cells, especially lithium ion cells, energy storage cells, a battery module with such energy storage cells, and a motor vehicle with such a battery module.
Batteries for storage of electric energy play a central role in the field of so-called electromobility both in vehicles with pure electric drive and in vehicles with hybrid drive. Usually one employs here high-voltage battery modules having many individual interconnected battery cells. The battery cells may be, for example, lithium, lithium ion, lithium polymer, lithium ion polymer, lithium sulfur or lithium air cells.
In the production of battery modules, the cells assembled into a cell pack are pressed together in a displacement-controlled manner. It may happen that, even if the specified cell thickness is maintained, a large variance may occur for the pressing forces, which may have a negative impact on the lifetime of the cells or the battery module.
The problem which the present invention proposes to solve is to indicate methods for producing energy storage cells, energy storage cells, a battery module, and a motor vehicle which are improved in terms of production and/or lifetime.
A method for producing an energy storage cell, especially a lithium ion cell, according to a first aspect of the invention has the following steps: introducing at least one electrode coil or electrode stack, having at least two electrodes and at least one separator arranged between the electrodes, into a housing; introducing an electrolyte into the housing; filling the housing with gas and generating an excess pressure in the housing, by which at least one housing wall of the housing is curved outward; and sealing the housing in a gas-tight manner, so that the excess pressure in the housing and the curvature of the at least one housing wall are maintained, so that the housing is elastically deformable in a direction perpendicular to the at least one curved housing wall.
A method for producing an energy storage cell, especially a lithium ion cell, according to a second aspect of the invention has the following steps: arranging at least one elastic element on an electrode coil or electrode stack having at least two electrodes, and introducing the electrode coil or electrode stack together with the at least one elastic element into a housing so that the at least one elastic element lies between the electrode coil or electrode stack and at least one housing wall of the housing, so that the housing is elastically deformable in a direction perpendicular to the at least one housing wall.
A method for producing a battery module has the following steps: producing two or more energy storage cells according to the first or second aspect of the invention; arranging the energy storage cells in a row or stacking them, especially in a direction perpendicular to the at least one housing wall; and compressing the row-arranged or stacked energy storage cells in a direction perpendicular to the at least one housing wall.
An energy storage cell according to the first aspect of the invention comprises: at least one electrode coil or electrode stack, having at least two electrodes and at least one separator arranged between the electrodes, and a housing, which surrounds the at least one electrode coil or electrode stack and in which an excess pressure prevails, by which at least one housing wall of the housing is curved outward, so that the housing is elastically deformable in a direction perpendicular to the at least one curved housing wall.
An energy storage cell according to the second aspect of the invention comprises: at least one electrode coil or electrode stack, having at least two electrodes and at least one separator arranged between the electrodes; at least one elastic element, as well as a housing, which surrounds the at least one electrode coil or electrode stack and the at least one elastic element arranged between the electrode coil or electrode stack and at least one housing wall of the housing, so that the housing is elastically deformable in a direction perpendicular to the at least one housing wall.
A battery module according to the invention comprises at least two interconnected energy storage cells according to the first and/or second aspect of the invention.
A motor vehicle according to the invention comprises an electric drive or a hybrid drive as well as a battery module according to the invention.
A motor vehicle in the sense of the present invention is preferably a land vehicle not permanently track-guided, especially a streetcar, such as a passenger car, a truck, a bus or a motorcycle, comprising in particular a hybrid or electric drive.
The invention is based on the notion of designing the energy storage cells to be elastic, especially resilient, in that the housing of the respective cell bulges outward by generating and maintaining an excess pressure inside the cell and/or at least one elastic element is provided between electrode coil or stack and housing wall. By selecting the gas pressure inside the cell or selecting the material and/or thickness of the elastic element, a specific reproducible spring characteristic can be adjusted for the elastic behavior of the respective cell.
Owing to the elastic, and especially resilient design, the cells exhibit a reproducible elastic spring behavior when the cell pack is compressed during the fabrication of the module. In this way, the relationship between geometry, especially thickness of the cells, and force behavior, especially compressing forces, can be taken into account when compressing the pack of cells. By monitoring or selecting the compressing forces during the fabrication of the module, the forces acting on the individual cells can be specifically adjusted, so that predetermined maximum forces can be reliably maintained, having a positive impact on the lifetime of the cells. In this way, the large variance for the forces occurring in the cell pack during the compression which occurs with conventional, non-elastically deformable cells can be reduced or even eliminated, so that a stable production process of modules with defined compressing forces is achieved. This also extends the lifetime of the cells or battery modules.
On the whole, this improves the energy storage cells and battery modules with such energy storage cells in terms of production and lifetime.
In one preferred embodiment of the method according to the first aspect of the invention, before the filling of the housing with gas, a gas initially present in the housing, especially air, is removed. In this way, a defined compressibility of the gas present in the housing can be assured and the required quantity of gas used to achieve the desired pressure in the interior of the housing can be clearly established. Furthermore, unwanted chemical reactions of the gas with the electrode coil or electrode stack or the housing itself can be prevented, such as might limit the lifetime of the cells.
In particular, it is advantageous when the housing is filled with an inert gas, for example nitrogen or carbon dioxide, in order to significantly reduce and/or slow down the likelihood of a reaction of the gas with the electrode coil or electrode stack or the housing itself.
In particular, it is advantageous when the inert gas used is a noble gas, for example helium, neon or argon. Their especially low reactivity has an especially advantageous effect on the lifetime of the energy storage cells and battery modules with such energy storage cells.
In another preferred embodiment of the method according to the first aspect of the invention, at least two opposite housing walls of the housing are curved outward by the filling of the housing with gas and the generating of an excess pressure. This preferably symmetrical curvature significantly facilitates the determination of the pressure point during the compression of the cell pack, so that the compressing forces during the compression of the cell pack can be specifically adjusted and/or monitored. Furthermore, a longer spring path per energy storage cell is formed in this way, making possible a more precise compression for the same force exerted.
Preferably in the case of a so-called prismatic cell, having a housing with two opposite large-area housing walls which are joined together by narrow side walls, the opposite large-area housing walls are curved outward, while the narrower side walls of the housing are not curved outward or only slightly curved outward.
In one preferred embodiment of the method according to the second aspect of the invention, the elastic element used is a layer of rubber, foam, or elastomer. Especially preferred here is a chemically inert material, in order to minimize or prevent chemical reactions with the electrode coil or electrode stack, the electrolyte, and/or the housing wall.
In one preferred embodiment of the battery module, the energy storage cells are designed to absorb the forces occurring during the production and/or during the operation of the battery module by virtue of the housing being elastically deformable in a direction perpendicular to the at least one housing wall. This has an advantageous effect on the lifetime of the energy storage cells of the battery module. Furthermore, the avoiding of peak forces on the energy storage cells of the battery module accomplished in this way ensures a reliable function as well as an enhanced operational security, which is of great importance especially for use in motor vehicles.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.